A wide range of medical treatments exist that utilize “endoluminal prostheses.” As used herein, endoluminal prostheses is intended to cover medical devices that are adapted for temporary or permanent implantation within a body lumen, including both naturally occurring and artificially-made lumens, such as without limitation, arteries or veins, whether located within the coronary, mesentery, peripheral, or cerebral vasculature, gastrointestinal tract, biliary tract, urethra, trachea, hepatic shunts, and fallopian tubes.
Accordingly, a wide assortment of endoluminal prostheses have been developed, each providing a uniquely beneficial structure to modify the mechanics of the targeted lumen wall. For example, stents are hollow, generally cylindrical devices that are known for implantation within body lumens to provide artificial radial support to wall tissue that forms the various lumens within the body, and often more specifically, for implantation within blood vessels of the body. Stents may function to hold open and/or expand a segment of the blood vessel, and are often used in the treatment of atherosclerosis in blood vessels. One method for treating atherosclerosis and other forms of vessel narrowing is percutaneous transluminal angioplasty, commonly referred to as “angioplasty,” “PTA” or “PTCA” when used in coronary arteries. The objective in angioplasty is to enlarge the lumen of the affected coronary artery by radial hydraulic expansion. The procedure is accomplished by inflating a balloon of a balloon catheter within the narrowed lumen of the coronary artery. In order to prolong the positive effects of PTCA and to provide radial support to the treated vessel, a stent may be implanted/deployed in conjunction with the procedure. Effectively, the stent overcomes the natural tendency of the vessel walls of some patients to close back down (“restenosis”), thereby maintaining a more normal flow of blood through that vessel than would be possible if the stent were not in place. A plastically deformable stent can be implanted during an angioplasty procedure by using a balloon catheter having a compressed or “crimped” stent loaded onto the balloon. The stent radially expands as the balloon is inflated, forcing the stent into contact with the body lumen, thereby forming a support for the vessel wall.
Deployment is effected after the stent has been percutaneously introduced and transluminally transported to be positioned at a desired location by means of the balloon catheter. Access to a treatment site is most often reached from the femoral artery. For treatment sites in small vessels that are remote from the insertion site, a flexible guiding catheter is inserted through an introducer sheath into the femoral artery. The guiding catheter is advanced through the vasculature to a treatment site, which may include advancement through the iliac artery, the ascending aorta and the aortic arch if the guiding catheter is to gain access to either the left or the right coronary artery, as desired. The procedure requires implantation of the stent, which has been loaded onto the balloon catheter, at a site remote from the insertion site, which means the stent is also guided through the potentially tortuous conduit of the vasculature to the treatment site. Therefore, the stent must be able to satisfy a number of mechanical requirements. First, the stent must possess sufficient flexibility to allow for crimping, expansion, and cyclic loading induced by the beating heart. Longitudinal flexibility is important to allow the stent to be maneuvered through a tortuous vascular path and to enable it to conform to a deployment site that may not be linear or may be subject to flexure. Second, the stent must be capable of withstanding the structural loads, namely radial compressive forces, imposed on the stent as it supports the walls of the vessel in which it is implanted. Therefore, a stent must possess adequate radial strength to maintain its size and shape throughout its service life despite the various forces that may come to bear on it, including the cyclic loading. For example, a radially directed force may tend to cause a stent to recoil inward, which is undesirable. Radial strength, which is the ability of a stent to resist radial compressive forces, is due to strength and rigidity around a circumferential direction of the stent. Radial strength and rigidity, therefore, may also be described as, hoop or circumferential strength and rigidity.
The structure of a stent is typically composed of scaffolding that includes a pattern or network of interconnecting structural elements often referred to in the art as struts. The scaffolding can be formed from wires, tubes, or sheets of material rolled into a cylindrical shape. The scaffolding is designed so that the stent has both flexibility, so as to be radially crimped onto the balloon catheter and advanced therewith through the vasculature, and radial strength, so as to be strong enough to provide radial support to the treatment site after implantation. Although there are innumerable stent designs that attempt to balance the competing requirements of flexibility and radial strength for use with stent delivery catheters, a need remains in the art for a stent delivery system that provides for deliverability and deployment of a stent such that the stent has a desirable balance of flexibility and radial strength.